The present invention generally pertains to gimbal systems and is particularly directed to an improvement in rate stabilizing, space-referenced gimbal platforms that support directional apparatus such as an antenna or a sensor.
In the prior art, the directional apparatus is mounted to a gimbal having a gyroscope mounted thereto so that the directional apparatus maintains the same orientation as the gyroscope. Gimbal systems are contained in vehicles, such as aircraft, missiles and ships, for use in navigation and/or guidance systems.
In prior art space-referenced, rate-stabilized gimbal systems, the gimbal platform is controlled by an angular rate servo loop system in response to a commanded rate signal that indicates a commanded rate of angular motion of the platform about a given axis. The rate of angular motion of the platform about the given axis is sensed by the gyroscope which provides a sensed rate signal indicating the sensed rate. The sensed rate signal is differentially compared with the commanded rate signal to provide an error signal indicating the difference between the compared rate signals. A rotary actuator, such as a torque motor, responds to the error signal by repositioning the platform with respect to the given axis until the error signal is less than a predetermined value. A two-axis gimbal platform could be controlled by two such rate servo loop systems.
Prior art gimbal platform systems also are controlled by angular position servo loop systems in response to a commanded position signal that indicates a commanded angular position of the platform with respect to a given axis. The angular position of the platform with respect to the given axis is sensed by a position transducer, such as a potentiometer coupled to the gimbal, to provide a sensed position signal indicating the sensed position. The sensed position signal is differentially compared with the commanded position signal to provide an error signal indicating the difference between the compared position signals. A rotary actuator responds to the error signal by repositioning the platform with respect to the given axis until the error signal is less than a given value. A two-axis gimbal platform could be controlled by two such position servo loop systems.
Gimbal platform systems contained in missiles support antennas and/or sensors for tracking targets in space. The gimbal system also must decouple the motion of the missile airframe from the motion of the platform-mounted antenna and/or sensor.
Tracking a target requires only a low frequency response by the antenna or sensor. However, decoupling the gimbal platform from airframe motion requires a high frequency response to airframe movements incident to transient missile maneuvers and airframe angular vibrations. Adequate decoupling at these higher frequencies is particularly important when an optical type of sensor is mounted on the platform since high frequency vibrations of the sensor can cause distortion or blurring of the sensed image.